iommu/arm-smmu: fix corner cases in address size calculations

Working out the usable address sizes for the SMMU is surprisingly tricky.
We must take into account both the limitations of the hardware for VA,
IPA and PA sizes but also any restrictions imposed by the Linux page
table code, particularly when dealing with nested translation (where the
IPA size is limited by the input address size at stage-2).

This patch fixes a few corner cases in our address size handling so that
we correctly deal with 40-bit addresses in TTBCR2 and restrict the IPA
size differently depending on whether or not we have support for nested
translation.

Change-Id: I66df2523bc60a87a5e9b260a7ce0bb4403b3237e
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: 4d09d99d543ec28b2280a1f62382697f47ea6366
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>